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IESD research paves the way for major revisions to the British Standard for daylight in buildings


September 2008

Design guidelines worldwide recommend daylight provision in terms of the long-established daylight factor (DF). Formulated in the UK over fifty years ago, the daylight factor is simply the ratio of internal illuminance to unobstructed horizontal illuminance under standard CIE overcast sky conditions. It is usually expressed as a percentage, so there is no consideration of absolute values. The luminance of the CIE standard overcast sky is rotationally symmetrical about the vertical axis, i.e. about the zenith. And, of course, there is no sun. Thus for a given building design, the predicted DF is insensitive to either the building orientation (due to the symmetry of the sky) or the intended locale (since it is simply a ratio). In other words, the predicted DF value would be the same if the building had North-facing glazing in Stornoway or South-facing glazing in Brighton. The same would be true if the locations were Moscow and Miami - or indeed for any city in any country.

The drive towards sustainable, low-energy buildings places increasing emphasis on detailed performance evaluation at the early design stage. The role that daylight evaluation plays in the design process has acquired a new impetus as the need to demonstrate compliance with various performance indicators becomes ever more pressing. Practitioners have become increasingly vociferous in their criticism of the standard method for daylight evaluation. Of particular concern is the lack of "realism" of the daylight factor approach and its fundamental inability to be part of an "holistic" solution that offered reliable, quantitative measures of actual daylight and which also informed on the effectiveness or otherwise of solar shading strategies, since the two are inextricably related.

Climate-based daylight modelling - pioneered by John Mardaljevic of the IESD - was formulated to overcome the limitations of the standard method. Climate-based modelling delivers predictions of absolute quantities (e.g. illuminance) that are dependent both on the locale (i.e. geographically-specific climate data is used) and the building orientation (i.e. the illumination effect of the sun and non-overcast sky conditions are included). It is now gaining acceptance as the most promising, perhaps even the only, line of research that will deliver truly effective design tools for the realistic evaluation of daylight in buildings.

Now firmly established as a leader in the in the research community, the first 'official' endorsement of the methods devised by Mardaljevic is the revision of British Standard 8206 ‘Daylight in Buildings’ (published September 2008). The single significant feature of this revision is a Technical Annex (drafted by Mardaljevic) on climate-based daylight modelling. This serves as a notification that the BSI expect future revisions to be founded on climate-based measures, and signals the first move away from the half-century-old standard method. A major programme of research will need to be carried out to formulate generalised daylight metrics that are founded on climate-based principles. Underpinning this research, Mardaljevic has applied climate-based daylight modelling to a number of live projects including: The New York Time Headquarters Building (USA), the Hermitage Museum (Russia) and a multi-climate evaluation of daylight in residential buildings for the VELUX corporation (based in Denmark).

 

IESD Commissions High Performance Computer Facility


September 2008

IESD has been studying building air flow using computer simulation methods for more than a decade. The work has included validation of software and application to real buildings. Computational Fluid Dynamics (CFD) methods continue to demand significant computing power. This is particularly so with modern techniques such as Large Eddy Simulation (LES). LES is an important research activity and enables further insight into airflow features such as thermal plumes as well as unsteady flows around buildings.

In order to develop its CFD research capabilities IESD has been able to procure a High Performance Computing facility with the aid of funding from the HEFCE Strategic Research Infrastructure Fund. The facility has been developed in partnership with Silicon Graphics Inc. and consists of a 32 node XE Linux Cluster. The cluster has 64 quad core Intel Xeon processors providing a total of 256 processor cores. The machine has more than 512 Gb of RAM and 3Tb of disk storage along with an ‘Infiniband®’ high speed interconnect system. The system represents a significant advance in the Institute’s research capabilities and will be used for computer modeling of air flow along with thermal comfort, daylighting and system operation in buildings.

HPCaltix

The High Performance Computer facility
consists of an SGI Altix XE Linux cluster
provided by Silicon Graphics Ltd.

 

plume

Development of a thermal plume
shown by a temperature isosurface
and calculated using LES methods.

 

IESD wins EPSRC funding for user responsive control of space heating


April 2008

Dr Mark Rylatt and Professor Li Shao at IESD have been successful in securing EPSRC funding for research into the energy efficiency of domestic space heating. They are members of an eight-university consortium "Carbon, Control and Comfort: user-centred control systems for comfort, carbon saving and energy management", which is led by the University of Reading. A special EPSRC panel in March ranked the consortium project (EP/G000395) first among the three proposals which resulted from the EPSRC/Eon Energy Efficiency Sand-pit event held last year.

Homes use around one third of the UK's energy, and produce around one third of all CO2 emissions. Identical homes with different occupants can vary in energy use by a factor of two to three. More effective, user responsive control can reduce the carbon footprint of a home much more than installing wind turbines or solar panels.

The overall aim of the project is to engage users in the design of control systems they like, that allow them to create the comfort conditions they want, and which through using the technology and fabric of their homes more effectively, reduce their energy use by 20%. It is estimated that this has the potential to save around 3 MT CO2 annually.

The 3-year £2 million consortium project is multidisciplinary with great emphasis on social-science research. The IESD provides a major technology input by developing an intelligent domestic energy agents concept which allows user responsive control of domestic heating systems. The work fits excellently with the user behaviour research carried out by other universities in the partnership

 

IESD In Sustainable Development Research 'Top 10'


February 2008

In January the Higher Education Funding Council for England (HEFCE) published its first Strategic Review of Sustainable Development in Higher Education in England. The Review of all 132 higher education institutions in England identified the 23 "main institutions engaged in SD research in England".

Based on activity at IESD, De Montfort University appears in sixth place in a ranking of these 23 based primarily on staff engagement and also on funding. Across the higher education sector the Review found that sustainable development activity has increased in recent years but is "very disparate".

One of the Review's key research questions concerned the relationship between research and teaching activities, on which it concluded: "SD research programmes are likely to stimulate SD pedagogy, while encouraging more effective SD pedagogy will both help define SD research agendas and ensure more high quality applications to SD research programmes when they are instituted". Such interaction between research and teaching is felt to be key to the success of the IESD.

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